GAE - How to filter on Datastore viewer using the Entity key or Primary

Search in you kind base record key

SELECT * FROM Kind WHERE __key__ = KEY('Kind', 'TheKeyValue')

Search on a kind base on the Parent key

SELECT * FROM Kind WHERE ANCESTOR IS KEY('ParentKind', 'ParentKeyWord')

Search all Entity base on Parent key what ever the Kind(See From Kind not exist)

SELECT * WHERE ANCESTOR IS KEY('ParentKind', 'ParentKeyWord')

More info hereGQL Syntax